Formula for/to calculate independently wealthy

[SpicyF]

Don't know if this is the right forum but i'll give it a shot. But it has something to do with stock market probarbly so why not.
Anyways, i'm looking for a forumla that will calculate how much money u need be able to invest and "live" on over a period of time. Let's say 50 years.
So 50 years you will need X amount of money each month. Let's say this amount is $3000, of course this amount must be changed accordingly to inflation.
So for 50 years, $3000 each month, with inflation, tax and everything how much would u need to invest to make it? (calculated with the growth % of the stock market in mind)

Replies would be appreciated as a 2 part answer, one for how much money you need if you still want to have the money left after 50 years and/or if your money is depleted in 50 years.

I sure hope someone understands and can help me with this problem. Sorry for bad english.